Apparatus and systems for harvesting energy in the form of vibrations and converting these into electrical energy for the purpose of powering electronic devices are well known. Most of these take advantage of the piezoelectric effect and power harvesting using piezoelectric materials has been investigated for various different applications.
It has been shown to be possible to harvest energy from walking using piezoelectric materials embedded in shoes and also in a backpack strap which generates electrical energy from the oscillating tension in the strap during walking. Systems have also demonstrated that it's possible to harvest energy from air flow, water currents and environmental vibrations, amongst other things, using piezoelectric materials.